Fatigue crack growth rate and tensile strength of Re modified Inconel 718 produced by means of selective laser melting

Abstract

The paper presents results of mechanical tests, namely fatigue crack growth (FCG) rate and tensile tests – of Inconel 718 produced by Selective Laser Melting (SLM) in pure form and with Re addition. SLM method was used to manufacture “comb like” structures, simulating small parts with thin walls, of which final mini-samples were cut out (two types of samples for tensile and one for the FCG rate test were used). A fraction of samples underwent a standard procedure of a heat treatment designed for Inconel 718 alloy. The influence of samples orientation to the laser beam direction, samples size and heat treatment on the tensile strength, yield strength and elongation to fracture were investigated. FCG rate tests were carried out using mini-samples with notches. Cyclic loading of samples was synchronized with CDD camera trigger for registering images of samples surfaces at the moments of maximal loading. Digital Image Correlation (DIC) was used to determine near crack tip displacement fields. The results of DIC measurements were analyzed using the inverse method to automatically determine the stress intensity factor and crack tip coordinates. Additionally, fracture surfaces SEM observations, X-ray Diffraction (XRD) analyses, X-ray fluorescence (XRF), light microscopy (LM) and Transmission Electron Microscopy (TEM) observations have been done to understand mechanical properties variation revealed during mechanical testing.